The present invention relates to a process for recovering wastes of a polymeric composition including a peroxidic crosslinking agent.
During the production of polymeric compositions including a peroxidic crosslinking agent—to be used, for instance, for the manufacturing of coating layers of electrical cables—remarkable amounts of wastes may result, e.g. because of formulation errors, contaminations or other undesired events that may modify composition and properties of the resulting polymeric material, making it unsuitable for the intended purpose. This is particularly critical in the case of polymeric compositions to be used for electrically insulating medium and/or high voltage electrical cables, wherein the insulating layer must be substantially devoid of any defects or impurities.
Polymeric wastes containing unreacted peroxidic crosslinking agent should be discarded following expensive national standard routes. It is environmentally preferable to recover such polymeric wastes, but the procedure poses several problems mainly because of the presence of the peroxidic crosslinking agent, which must be eliminated so as to avoid any undesired crosslinking of the composition during the subsequent processing of the recovered material. It is worthwhile to note that a direct recycling of the wastes to the production process of the composition is not feasible, since it is practically impossible to determine with sufficient precision the composition of the wastes, particularly as regards the peroxide content, a parameter that shall be known with high accuracy to carry out the process for manufacturing, for example, electrical cables in a reliable manner.
In patent application JP 62-20244 a method is disclosed for recycling an uncrosslinked crystalline polyolefin resin composition containing an organic peroxide by thermally decomposing the organic peroxide without causing the crosslinking of the composition by: (i) applying pressure to the composition so as to elevate the melting point of the crystalline polyolefin resin above the thermal decomposition temperature of the peroxide; and (ii) heating the composition to a temperature between the elevated melting point and the decomposition temperature.
U.S. Pat. No. 4,123,584 (Southwire Co.) relates to a process for recovering scrap thermosetting plastic compounds which comprises the steps of first hot-granulating the fresh scrap compound before it has time to fully cure, allowing the granules to cool, thereby arresting any further curing of the compound, then further processing the granules into a fine powder. The fine powder can be reused directly or blended with virgin material.
According to the Applicant, the above processes are substantially ineffective and difficult to carry out on an industrial scale, since they require a very accurate thermal control of the polymeric mass during the waste processing, a control that is difficult to achieve particularly when large polymeric masses are to be treated.